Display device and luminance control method therefor

ABSTRACT

A temperature difference estimated value is found from a video signal using a temperature estimated value representing the temperature of the panel outer periphery of a display screen of a PDP and a reference value representing the temperature of the panel outer periphery of the PDP which is outputted from a panel periphery temperature setter by a temperature difference estimator, and the luminance of an image displayed on a display is controlled depending on the temperature difference estimated value by a controller and a brightness controller.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 09/856,161, filed Jun.1, 2001, which was the National Stage of International Application No.PCT/JP00/06212, filed Sep. 11, 2000, the contents of which are expresslyincorporated by reference herein in their entireties. The InternationalApplication was not published under PCT Article 21(2) in English.This isreissue application of U.S. application Ser. No. 09/994,794, filed onNov. 28, 2001, now U.S. Pat. No. 6,441,803, which is a divisional ofU.S. application Ser. No. 09/856,161, filed Jun. 1, 2001, now U.S. Pat.No. 6,414,660, which was the National Stage of International ApplicationNo. PCT/JP00/06212, filed Sep. 11, 2000, the contents of which areexpressly incorporated by reference herein in their entireties. TheInternational Application was not published under PCT Article 21( 2 ) inEnglish.

TECHNICAL FIELD

The present invention relates to a display device for displaying animage with luminance corresponding to a video signal inputted from theexterior and a luminance control method therefore.

BACKGROUND ART

Plasma display devices using PDPs (Plasma Display Panels) have theadvantage that thinning and larger screens are possible. In the plasmadisplay devices, images are displayed by utilizing light emission incases where discharge cells composing pixels are discharged. As light isthus emitted, heat is generated on a glass surface composing the PDP, sothat the higher the luminance of-an image. becomes, the larger theamount of heat generation becomes. Therefore, the temperature of theglass surface is raised. In the worst case, the glass surface isdamaged.

In order to solve the above-mentioned problem, an example of aconventional display device is a display device disclosed inJP-A-11-194745. In the display device, the whole surface of a displayscreen is divided into a plurality of blocks, temperature estimatedvalues are calculated with respect to all the blocks, and the maximumvalue of the calculated estimated temperatures is compared with areference temperature to produce a luminance correction coefficient. Theluminance of the display screen is controlled by the luminancecorrection coefficient.

A display on which an image is displayed is generally fixed in its outerperiphery. Damage to the display caused by the rise in the temperaturewith the increase in the luminance may occur in the vicinity of theouter periphery of the display in most cases. That is, the damage to thedisplay depends on the temperature difference rather than the maximumtemperature. Generally, the temperature difference between the outerperiphery of the display where no heat is generated and the outerperiphery of the display screen of the display where heat is generatedis the largest. The display may be damaged by thermal stress created bythe temperature difference in many cases.

In the conventional display device, however, only when the maximum valueof the estimated temperatures reaches not less than the referencetemperature, that is, when the temperature of any portion on the displayscreen exceeds its certain upper-limit value, the luminance iscontrolled.

Therefore, the luminance cannot be always controlled when excessivethermal stress is exerted on the outer periphery, which is most easilydamaged, of the display, thereby making it impossible to reliablyprevent the display from being damaged.

In the conventional display device, the whole of the display screen isdivided into a plurality of blocks, and the estimated temperatures arecalculated with respect to all the blocks. Accordingly, operationprocessing becomes complicated, and long time is required to perform theoperation processing. Particularly in recent years, it has been desiredto make a display image highly precise. The number of pixels composingthe display screen, that is, the number of discharge cells has tended tobe increased. In this case, the above-mentioned operation processing hasincreasingly become complicated, and the processing time is lengthened.

DISCLOSER OF INVENTION

An object of the present invention is to provide a display devicecapable of more reliably preventing a display from being damaged and aluminance control method therefore.

Another object of the present invention is to provide a display devicecapable of more reliably preventing a display from being damaged in asmall amount of operation and a luminance control method therefore.

A display device according to an aspect of the present inventioncomprises a display for displaying an image with luminance correspondingto a video signal inputted from the exterior; a temperature estimationcircuit for estimating from the video signal a temperature estimatedvalue corresponding to the temperature of a display screen of thedisplay; an operation circuit for finding a temperature differenceestimated value using a reference value corresponding to the temperatureof the outer periphery of the display and the temperature estimatedvalue; and a control circuit for controlling the luminance of the imagedisplayed on the display on the basis of the temperature differenceestimated value.

In the display device, the temperature estimated value corresponding tothe temperature of the display screen of the display is estimated fromthe video signal, and the temperature difference estimated value isfound using the temperature estimated value and the reference valuecorresponding to the temperature of the outer periphery of the display,to control the luminance of the image displayed on the display on thebasis of the temperature difference estimated value. Generally, thedisplay on which the image is displayed is fixed in its outer periphery.Accordingly, damage to the display caused by the rise in the temperaturewith the increase in the luminance may occur in the vicinity of theouter periphery of the display in most cases. Therefore, the luminanceis controlled depending on the temperature difference estimated valuefound from the temperature estimated value corresponding to thetemperature of the display screen and the temperature of the outerperiphery of the display, as described above, so that the luminance canbe controlled on the basis of the temperature difference between theouter periphery of the display which most greatly affects the damage tothe display and the display screen, thereby making it possible to morereliably prevent the display from being damaged.

It is preferable that the temperature estimation circuit estimates thetemperature estimated value corresponding to the temperature of theouter periphery of the display screen of the display.

In this case, the temperature difference estimated value correspondingto the temperature of the outer periphery of the display screen of thedisplay is estimated from the video signal, and the temperaturedifference estimated value is found using the temperature estimatedvalue and the reference value corresponding to the temperature of theouter periphery of the display, to control the luminance of the imagedisplayed on the display on the basis of the temperature differenceestimated value. The temperature difference estimated value is foundfrom the temperature estimated value corresponding to the temperature ofthe outer periphery of the display screen and the reference valuecorresponding to the temperature of the outer periphery of the display.Accordingly, the luminance can be controlled on the basis of thetemperature difference between the outer periphery of the display whichgreatly affects the damage to the display and the outer periphery of thedisplay screen closest to the outer periphery, thereby making itpossible to more reliably prevent the display from being damaged.Further, the temperature estimated value operated in order to find thetemperature difference estimated value is limited to the temperatureestimated value for the outer periphery of the display screen of thedisplay. Accordingly, the amount of operation is made smaller than thatin a case where the temperature estimated value on the whole of thedisplay screen, so that the processing is simplified, and the processingtime is shortened. As a result, it is possible to more reliably preventthe display from being damaged in a small amount of operation.

It is preferable that the display comprises first and second boardsbetween which a plurality of light emitting elements are formed and towhich its outer periphery is fixed, and the outer periphery of thedisplay includes a portion between the light emitting element positionedin the outermost periphery out of the plurality of light emittingelements and a fixed portion of the first and second boards.

In this case, the reference value corresponds to the temperature of theportion between the light emitting element positioned in the outermostperiphery and the fixing portion of the first and second boards.Accordingly, the luminance can be controlled using as a basis thetemperature of the portion most easily damaged, thereby making itpossible to more reliably prevent the display from being damaged.

It is preferable that the temperature estimation circuit estimates thetemperature estimated value by integrating data relating to theluminance from the video signal and subtracting the amount of dissipatedheat therefrom, and the operation circuit subtracts the reference valuefrom the temperature estimated value, to find the temperature differenceestimated value.

In this case, the data relating to the luminance is integrated from thevideo signal, and the amount of dissipated heat is subtracted therefrom,thereby making it possible to find the temperature estimated valuecorresponding to the truer temperature. Consequently, the luminance iscontrolled on the basis of the temperature difference estimated valueobtained by subtracting the reference value from the temperatureestimated value. Accordingly, it is possible to control the luminancewith higher precision to more reliably prevent the display from beingdamaged.

It is preferable that the control circuit lowers the luminance of theimage displayed on the display with the increase in the temperaturedifference estimated value.

In this case, the luminance is lowered with the increase in thetemperature difference estimated value, thereby making it possible tomore reliably prevent the display from being damaged.

It is preferable that the control circuit lowers the maximum luminanceof the image displayed on the display with the increase in thetemperature difference estimated value.

In this case, the maximum luminance is lowered with the increase in thetemperature difference estimated value, thereby making it possible tomore reliably prevent the display from being damaged as well as makingit possible to display, when the luminance other than the maximumluminance is displayed as it is, a good image corresponding to theluminance of the video signal itself.

It is preferable that the display displays the image with a gray scalecorresponding to the video signal out of a plurality of gray scales, andthe control circuit lowers the luminance of the image displayed on thedisplay at the same ratio for each of the gray scales.

In this case, the luminance is lowered at the same ratio for each grayscale, thereby making it possible to lower the luminance of the displaywithout giving a visually uncomfortable feeling to a viewer.

It is preferable that the display displays the image with a gray scalecorresponding to the video signal using a plurality of light emittingformats which are the same in the total number of gray scales and differin the number of light emitting pulses on each of the gray scales, andthe control circuit controls the luminance of the image displayed on thedisplay using the light emitting format selected depending on thetemperature difference estimated value out of the plurality of lightemitting formats.

In this case, the luminance can be controlled by switching the pluralityof light emitting formats in the order of their decreasing numbers oflight emitting pulses on the same gray scale with the increase in thetemperature difference estimated value, thereby making it possible tolower the luminance without greatly changing the total number of grayscales.

It is preferable that the control circuit divides the display screen ofthe display into a plurality of blocks, extracts from the plurality ofblocks the peripheral block adjacent to the outer periphery of thedisplay screen, and lowers the luminance of the peripheral block.

In this case, the luminance of the peripheral block adjacent to theouter periphery of the display screen is lowered. Accordingly, the imagein the block inside the display screen can be displayed with theluminance of the video signal itself, thereby making it possible toprovide a display screen having no visually uncomfortable feeling by theviewer as well as to more reliably prevent the outer periphery of thedisplay from being damaged.

It is preferable that the control circuit divides a display screen ofthe display into a plurality of blocks, extracts from the plurality ofblocks the peripheral block adjacent to the outer periphery of thedisplay screen, and makes the luminance of the peripheral block lowerthan that of the block inside the display screen of the display.

In this case, the luminance of the peripheral block is made lower thanthat of the block inside the display screen. Accordingly, the luminanceof the display screen is smoothly changed, thereby making it possible toprovide a display screen having no visually uncomfortable feeling by theviewer as well as to more reliably prevent the outer periphery of thedisplay from being damaged.

It is preferable that the display device further comprises a blockextraction circuit for dividing the display screen of the display into aplurality of blocks and extracting from the plurality of blocks theperipheral blocks adjacent to the outer periphery of the display screen,the temperature estimation circuit estimates the temperature estimatedvalues for the peripheral blocks, the operation circuit finds aperipheral block temperature difference estimated value from thetemperature estimated values estimated for the peripheral blocks, andthe control circuit controls the luminance for each of the peripheralblocks on the basis of the peripheral block temperature differenceestimated value.

In this case, the display screen is divided into the plurality ofblocks, and the luminance is controlled for each of the peripheralblocks adjacent to the outer periphery of the display screen.Accordingly, the luminance can be controlled more finely, thereby makingit possible to provide a display screen having no visually uncomfortablefeeling by the viewer as well as to more reliably prevent the outerperiphery of the display from being damaged.

It is preferable that the control circuit controls the luminance foreach of the peripheral blocks such that the amount of controlledluminance between the adjacent peripheral blocks is smoothly changed onthe basis of the peripheral block temperature difference estimatedvalue.

In this case, the amount of controlled luminance between the adjacentperipheral blocks is smoothly changed. Accordingly, a display screenhaving no visually uncomfortable feeling can be provided for the viewer,and thermal stress created in the outer periphery of the display issmoothly changed, thereby making it possible to more reliably preventthe display from being damaged.

It is preferable that the display device further comprises a blockextraction circuit for dividing the display screen of the display into aplurality of blocks and extracting from the plurality of blocks theperipheral blocks adjacent to the outer periphery of the display screen,the temperature estimation circuit estimates the temperature estimatedvalues for the peripheral blocks, the operation circuit finds, out ofthe temperature estimated values estimated for the peripheral blocks,peripheral block temperature difference estimated values for theperipheral blocks, and extracts from the peripheral block temperaturedifference estimated values the maximum peripheral block temperaturedifference estimated value, and the control circuit controls theluminance of the image displayed on the display on the basis of themaximum peripheral block temperature difference estimated value.

In this case, the luminance is controlled using the maximum peripheralblock temperature difference estimated value representing the largesttemperature difference in the peripheral blocks, thereby making itpossible to more reliably prevent the display from being damaged.Further, the luminance is controlled by the maximum peripheral blocktemperature difference estimated value, thereby simplifying processingfor controlling the luminance.

It is preferable that the reference value includes a plurality ofreference values which differ depending on the position of the outerperiphery of the display.

In this case, the luminance of the image displayed on the display can becontrolled using the plurality of reference values which differdepending on the position of the outer periphery of the display.Accordingly, a high reference value is set in a portion where thetemperature is easily raised, while a low reference value is set in aportion where the temperature is not easily raised, thereby making itpossible to control the luminance on the basis of each of the referencevalues. As a result, the display can be more reliably prevented frombeing damaged, and the luminance is not lowered any more than necessary.

It is preferable that the display device further comprises a measurementcircuit for measuring the temperature of the outer periphery of thedisplay and outputting to the operation circuit the reference valuecorresponding to the measured temperature.

In this case, the temperature of the outer periphery of the display isdirectly measured, thereby making it possible to control the luminanceon the basis of the reference value corresponding to the temperature.Even when the reference value is changed by the variation in outside airtemperature, for example, it is possible to reliably prevent the displayfrom being damaged.

A luminance control method for a display device according to anotheraspect of the present invention is a luminance control method for adisplay device comprising a display for displaying an image withluminance corresponding to a video signal inputted from the exterior,characterized by comprising the steps of estimating from the videosignal a temperature estimated value corresponding to the temperature ofa display screen of the display; finding a temperature differenceestimated value using a reference value corresponding to the temperatureof the outer periphery of the display and the temperature estimatedvalue; and controlling the luminance of the image displayed on thedisplay on the basis of the temperature difference estimated value.

In the luminance control method for the display device, the temperatureestimated value corresponding to the temperature of the display screenof the display is estimated from the video signal, and the temperaturedifference estimated value is found using the temperature estimatedvalue and the reference value corresponding to the temperature of theouter periphery of the display, to control the luminance of the imagedisplayed on the display on the basis of the temperature differenceestimated value. Generally, the display on which the image is displayedis fixed in its outer periphery. The damage to the display caused by theincrease in the luminance may occur in the vicinity of the outerperiphery of the display in most cases. Consequently, the luminance iscontrolled depending on the temperature difference estimated value foundfrom the temperature estimated value corresponding to the temperature ofthe display screen and the reference value corresponding to thetemperature of the outer periphery of the display, thereby making itpossible to control the luminance on the basis of the temperaturedifference between the outer periphery of the display which most greatlyaffects the damage to the display and the display screen and to morereliably prevent the display from being damaged.

It is preferable that the temperature estimating step comprises the stepof estimating the temperature estimated value corresponding to thetemperature of the outer periphery of the display screen of the display.

In this case, the temperature estimated value corresponding to thetemperature of the outer periphery of the display screen of the displayis estimated from the video signal, and the temperature differentestimated value is found using the temperature estimated value and thereference value corresponding to the temperature of the outer peripheryof the display, to control the luminance of the image displayed on thedisplay on the basis of the temperature difference estimated value. Thetemperature difference estimated value is found from the temperatureestimated value corresponding to the temperature of the outer peripheryof the display screen and the reference value corresponding to thetemperature of the outer periphery of the display. Accordingly, theluminance can be controlled on the basis of the temperature differencebetween the outer periphery of the display which most greatly affectsthe damage to the display and the outer periphery of the display screenclosest to the outer periphery of the display, thereby making itpossible to more reliably prevent the display from being damaged.Further, the temperature estimated value operated in order to find thetemperature difference estimated value is limited to the temperatureestimated value for the outer periphery of the display screen of thedisplay. Accordingly, the amount of operation is made smaller than thatin a case where the temperature estimated value on the whole of thedisplay screen is operated, so that the processing is simplified, andthe processing time is shortened. As a result, it is possible to morereliably prevent the display from being damaged in a small amount ofoperation.

It is preferable that the display displays the image on a gray scalecorresponding to the video signal using a plurality of light emittingformats which are the same in the total number of gray scales and differin the number of light emitting pulses on each of the gray scales, andthe controlling step comprises the step of controlling the luminance ofthe image displayed on the display using the light emitting formatselected depending on the temperature difference estimated value out ofthe plurality of light emitting formats.

In this case, the luminance can be controlled by switching the pluralityof light emitting formats in the order of their decreasing numbers oflight emitting pulses on the same gray scale with the increase in thetemperature difference estimated value, thereby making it possible tolower the luminance without greatly changing the total number of grayscales.

It is preferable that the controlling step comprises the step ofdividing the display screen of the display into a plurality of blocks,extracting from the plurality of blocks the peripheral blocks adjacentto the outer periphery of the display screen, and lowering the luminanceof the peripheral blocks.

In this case, the luminance of the peripheral blocks adjacent to theouter periphery of the display screen is lowered. Accordingly, the imagein the block inside the display screen can be displayed with theluminance of the video signal itself, thereby making it possible toprovide a display screen having no visually uncomfortable feeling by theviewer as well as to more reliably prevent the outer periphery of thedisplay from being damaged.

It is preferable that the luminance control method for the displaydevice further comprises the step of dividing the display screen of thedisplay into a plurality of blocks and extracting from the plurality ofblocks the peripheral blocks adjacent to the outer periphery of thedisplay screen, the temperature estimating step comprises the step ofestimating the temperature estimated values for the peripheral blocks,the temperature difference estimated value operating step comprises thestep of finding a peripheral block temperature difference estimatedvalue from the temperature estimated values estimated for the peripheralblocks, and the controlling step comprises the step of controlling theluminance for each of the peripheral blocks on the basis of theperipheral block temperature difference estimated value.

In this case, the display screen is divided into the plurality ofblocks, and the luminance is controlled for each of the peripheralblocks adjacent to the outer periphery of the display screen.Accordingly, the luminance can be controlled more finely, thereby makingit possible to provide a display screen having no visually uncomfortablefeeling by the viewer as well as to more reliably prevent the outerperiphery of the display from being damaged.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a plasma displaydevice according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a temperaturedifference estimator shown in FIG. 1.

FIG. 3 is a block diagram showing the configuration of a brightnesscontroller shown in FIG. 1.

FIG. 4 is a block diagram showing the configuration of a display shownin FIG. 1.

FIG. 5 is a schematic view showing the configuration of a PDP shown inFIG. 4.

FIG. 6 is a diagram showing sub-fields used for each gray scale level ina case where an image is displayed on 256 gray scales.

FIG. 7 is a diagram showing the respective numbers of light emittingpulses in each sub-field in different light emitting formats.

FIG. 8 is a diagram showing the relationship between a temperaturedifference estimated value and a multiplication factor in a case wherelight emitting formats A to E shown in FIG. 7 are used.

FIG. 9 is a diagram showing the relationship between a temperaturedifference estimated value and luminance after control in a case wherethe temperature difference estimated value and the multiplication factorshown in FIG. 8 are used.

FIG. 10 is a diagram showing the relationship between a temperaturedifference estimated value and a multiplication factor in a case where alight emitting format A shown in FIG. 7 is used.

FIG. 11 is a diagram for explaining a second luminance control methodfor the plasma display device shown in FIG. 1.

FIG. 12 is a diagram for explaining a third luminance control method forthe plasma display device shown in FIG. 1.

FIG. 13 is a block diagram showing the configuration of a plasma displaydevice according to a second embodiment of the present invention.

FIG. 14 is a block diagram showing the configuration of a temperaturedifference estimator shown in FIG. 13.

FIG. 15 is a diagram showing an example of a temperature estimated valueand a peripheral block temperature difference estimated value which areestimated for each peripheral block.

FIG. 16 is a diagram showing an example of a peripheral blocktemperature difference estimated value and a multiplication factor by afirst luminance control method for the plasma display device shown inFIG. 13.

FIG. 17 is a diagram showing an example of a peripheral blocktemperature difference estimated value, a peripheral lock temperaturedifference estimated value after filtering processing, and amultiplication factor by a second luminance control method for theplasma display device shown in FIG. 3.

FIG. 18 is a block diagram showing the configuration of plasma displaydevice according to a third embodiment of the present invention.

FIG. 19 is a block diagram showing the configuration of a temperaturedifference estimator shown in FIG. 18.

FIG. 20 is a diagram showing an example of a temperature differenceestimated value, a peripheral block temperature difference estimatedvalue, and a maximum peripheral block temperature difference estimatedvalue which are estimated for each peripheral block.

FIG. 21 is a block diagram showing the configuration of a plasma displaydevice according to a fourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An AC-type plasma display device will be described as an example of adisplay device according to the present invention. A display device towhich the present invention is applied is not particularly limited tothe AC-type plasma display device. The present invention is similarlyapplicable to another display device, provided that the temperature of adisplay screen is changed by a change in luminance.

A plasma display device according to a first embodiment of the presentinvention will be first described. FIG. 1 is a block diagram showing theconfiguration of the plasma display device according to the firstembodiment of the present invention.

The plasma display device shown in FIG. 1 comprises a display 1, abrightness controller 2, a controller 3, a temperature differenceestimator 4, and a panel periphery temperature setter 5.

A video signal VS is inputted to the brightness controller 2 and thetemperature difference estimator 4. The panel periphery temperaturesetter 5 sets a reference value To representing the temperature of thepanel outer periphery of the display 1, and outputs the reference valueTo to the temperature difference estimator 4. The temperature differenceestimator 4 calculates a temperature difference estimated value Tdrepresenting the difference between the temperature of the panel outerperiphery of the display 1 and the temperature of the display screen ofthe display 1 using the video signal VS and the reference value To, andoutputs the temperature difference estimated value Td to the controller3.

The controller 3 outputs to the brightness controller 2 a brightnesscontrol signal LC for controlling the luminance of the display screen ofthe display 1 depending on the temperature difference estimated valueTd. The brightness controller 2 outputs to the display 1 a data driverdriving control signal DS, a scan driver driving control signal CS, anda sustain driver driving control signal US for displaying an image withluminance corresponding to the brightness control signal LC.

FIG. 2 is a block diagram showing the configuration of the temperaturedifference estimator 4 shown in FIG. 1. As shown in FIG. 2, thetemperature difference estimator 4 comprises a periphery adjacentportion separator 41, an integration circuit 42, a dissipated heatsubtraction circuit 43, and a subtracter 44.

The periphery adjacent portion separator 41 receives the video signalVS, separates from the video signal VS a portion of a periphery adjacentportion adjacent to the outer periphery of the display screen of thedisplay 1 from the video signal VS and outputs the separated portion tothe integration circuit 42. The video signal VS includes not only aninherent video signal but also a vertical synchronizing signal, ahorizontal synchronizing signal, and so forth. The periphery adjacentportion is separated using the horizontal synchronizing signal, thevertical synchronizing signal, and so forth.

The integration circuit 42 integrates data relating to luminance fromthe video signal for the periphery adjacent portion separated by theperiphery adjacent portion separator 41, for example, a luminance signalfor the periphery adjacent portion, and outputs the integrated luminancesignal to the dissipated heat subtraction circuit 43.

The dissipated heat subtraction circuit 43 subtracts the amount ofdissipated heat from the integrated luminance signal for the peripheryadjacent portion to calculate a temperature estimated value Terepresenting the temperature of the periphery adjacent portion, andoutputs the temperature estimated value Te to the subtracter 44.

The subtracter 44 subtracts the reference value To for the panel outerperiphery from the temperature estimated value Te for the peripheryadjacent portion to find a temperature difference estimated value Td forthe outer periphery of the display screen, and outputs the temperaturedifference estimated value Td to the controller 3.

The controller 3 selects, out of a plurality of light emitting formats,the corresponding light emitting format depending on the temperaturedifference estimated value Td found by the processing, generates abrightness control signal LC including a light emitting pulse controlsignal EC for designating the selected light emitting format and amultiplication factor k in the selected light emitting format, andoutputs the generated brightness control signal LC to the brightnesscontroller 2.

FIG. 3 is a block diagram showing the configuration of the brightnesscontroller 2 shown in FIG. 1. As shown in FIG. 3, the brightnesscontroller 2 comprises a multiplication circuit 21, a videosignal/sub-field corresponder 22, and a sub-field pulse generator 23.

The multiplication circuit 21 multiplies the video signal VS by themultiplication factor k included in the brightness control signal LC,and outputs to the video signal/sub-field corresponder 22 a video signalwhose luminance has been controlled by the multiplication factor k.

The video signal/sub-field corresponder 22 divides one field into aplurality of sub-fields to perform display.

Accordingly, it generates from a video signal corresponding to one fieldimage data for each sub-field in the light emitting format designatedfrom the plurality of light emitting formats in response to the lightemitting pulse control signal EC included in the brightness controlsignal LC, and outputs a data driver driving control signal DCcorresponding to the image data for each sub-field to the display 1.

The sub-field pulse generator 23 outputs to the display 1 the scandriver driving control signal CS and the sustain driver driving controlsignal US which correspond to each sub-field in the light emittingformat designated from the plurality of light emitting formats inresponse to the light emitting pulse control signal EC included in thebrightness control signal LC.

FIG. 4 is a block diagram showing the configuration of the display 1shown in FIG. 1. The display shown in FIG. 1 comprises a PDP (PlasmaDisplay Panel) 11, a data driver 12, a scan driver 13, and a sustaindriver 14.

The data driver 12 is connected to a plurality of address electrodes(data electrodes) AD in the PDP 11. The scan driver 13 contains drivingcircuits respectively provided for scan electrodes SC in the PDP 11, andeach of the driving circuits is connected to the corresponding scanelectrode SC. The sustain driver 14 is together connected to a pluralityof sustain electrodes SU in the PDP 11.

The data driver 12 applies a write pulse to the corresponding addresselectrode AD in the PDP 11 during a write time period in accordance withthe data driver driving control signal DS. On the other hand, the scandriver 13 successively applies the write pulses to the plurality of scanelectrodes SC in the PDP 11 while shifting a shift pulse in the verticalscanning direction during the write time period in accordance with thescan driver driving control signal CS. Consequently, address dischargesare induced in the corresponding discharge cell, and the discharge cellcorresponding to the video signal VS is selected.

The scan driver 13 applies periodical sustain pulses to the plurality ofscan electrodes SC in the PDP 11 during a sustain time period inaccordance with the scan driver driving control signal CS. On the otherhand, the sustain driver 14 simultaneously applies sustain pulses whichare shifted in phase by 180° from the sustain pulses applied to the scanelectrodes SC in the sustain time period in accordance with the sustaindriver driving control signal US. Consequently, sustain discharges areinduced in the discharge cell selected in an address time period, and animage is displayed on the display screen with luminance corresponding tothe video signal VS.

FIG. 5 is a schematic view showing the configuration of the PDP 11 shownin FIG. 4. As shown in FIG. 5, the PDP 11 comprises a plurality ofaddress electrodes AD, a plurality of scan electrodes SC, a plurality ofsustain electrodes SU, a surface glass board FP, a reverse glass boardBP, and a barrier wall WA.

The plurality of address electrodes AD are arranged in the verticaldirection on the screen, and the plurality of scan electrodes SC and theplurality of sustain electrodes SU are arranged in the horizontaldirection on the screen. Further, the sustain electrodes SU are togetherconnected. A discharge cell CE is formed at each of the intersections ofthe address electrodes AD, the scan electrodes SC, and the sustainelectrodes SU. Each of the discharge cells CE composes a pixel on thescreen.

Furthermore, the scan electrodes SC and the sustain electrodes SU areformed in the horizontal direction on the screen such that they arepaired on the surface glass board FP, and are covered with a transparentdielectric layer and a protective layer. On the other hand, the addresselectrodes AD are formed in the vertical direction on the screen on thereverse glass board BP opposite to the surface glass board FP, atransparent dielectric layer is formed thereon, and a fluorescent memberis further applied thereon. The barrier wall WA is provided between theaddress electrodes AD, so that the adjacent discharge cells CE areseparated from each other. When color display is performed, the addresselectrodes AD are provided every R, G; and B, and the barrier wall WA isprovided between the address electrodes AD.

The surface glass board FP and the reverse glass board BP are fixed withtheir outer peripheries joined to each other by a sealing glass SG. Whenthe temperatures of the surface glass board FP and the reverse glassboard BP are raised by causing the display cells CE to emit light,cracks occur in the vicinity of the sealing glass SG for the surfaceglass board FP and the reverse glass board BP. Consequently, the PDP 11may be damaged in many cases. In the present embodiment, the luminanceof the PDP 11 is controlled on the basis of the temperature differencein the portion most easily damaged. Therefore, the temperaturedifference estimated value Td is found in the following manner.

A portion, including at least the discharge cells CE positioned in theoutermost periphery (for example, a square frame portion indicated byhatching), of the display screen of the PDP 11, that is, a portion wherethe discharge cells CE are formed is taken as a periphery adjacentportion NE, to separate a video signal in the region by the peripheryadjacent portion separator 41 in the temperature difference estimator 4.The separated video signal is integrated, for example, by theintegration circuit 42 and the dissipated heat subtraction circuit 43,to find a temperature estimated value Te representing the temperature ofthe periphery adjacent portion NE.

On the other hand, the panel periphery temperature setter 5 takes aportion of the sealing glass SG for the surface glass board FP and thereverse glass board BP and a portion between the discharge cell CEpositioned in the outermost periphery and the sealing glass SG as thepanel outer periphery, and sets the temperature of the portion as areference value To. Consequently, the reference value To for the panelouter periphery is subtracted from the temperature estimated value Tefor the periphery adjacent portion NE, thereby operating the temperaturedifference estimated value Td for the outer periphery of the displayscreen. Consequently, the luminance is controlled, as described later,using the temperature difference estimated value Td representing thetemperature difference in the portion most easily damaged, thereby morereliably preventing the PDP 11 form being damaged.

In the present embodiment, the PDP 11 corresponds to a display, thetemperature difference estimator 4 corresponds to a temperatureestimation circuit and an operation circuit, and the brightnesscontroller 2, the controller 3, the data driver 12, the scan driver 13,and the sustain driver 14 correspond to a control circuit. Further, theperiphery adjacent portion separator 41, the integration circuit 42, andthe dissipated heat subtraction circuit 43 correspond to a temperatureestimation circuit, and the subtracter 44 corresponds to an operationcircuit.

Description is now made of a gray scale display method using five typesof light emitting formats in which the total number of gray scales is256, and one field is divided into eight sub-fields to perform displayas an example of a gray scale display method for the display deviceconfigured as described above. The gray scale display method to whichthe present invention is applied is not particularly limited to thefollowing example. Another gray scale display method may be used.

FIG. 6 is a diagram showing sub-fields where sustain discharges shouldbe induced when the display screen is displayed at each gray scale levelin a case where the total number of gray scales is 256. In FIG. 6, thesub-fields SF1 to SF8 are successively respectively weighted withbrightness values 1, 2, 4, 8, 16, 32, 64, and 128, for example. Each ofthe weights is a value proportional to the luminance of the displayscreen, for example, the number of times of light emission in each ofthe discharge cells.

In FIG. 6, the sub-fields SF1 to SF8 used for causing the discharge cellto emit light at each gray scale level are indicated by o. In order tocause the discharge cell to emit light at a gray scale level 1, thesub-field SF1 (a weight 1) may be used. In order to cause the dischargecell to emit light at a gray scale level 3, the sub-field SF1 and thesub-field SF2 (a weight 2) may be used, and a corresponding column ineach of the sub-fields is assigned o. If the sub-fields are combinedwith each other to cause the discharge cell to emit light in a number oftimes of light emission corresponding to the weight, gray scale displaycan be performed at each of the gray scale levels 0 to 255. The numberof sub-fields obtained by the division, the weights, and so forth arenot particularly limited to those in the abovementioned example, andvarious modifications are possible.

Description is now made of five types of light emitting formats in whichthe total number of gray scales is 256 as an example of a light emittingformat using the sub-fields SF1 to SF8 which are weighted as describedabove.

FIG. 7 is a diagram showing the number of light emitting pulses in eachof the sub-fields SF1 to SF8 in each of the five types of light emittingformats A to E. Each of the light emitting formats A to E is determinedby the controller 2 depending on the temperature estimated value Td, asdescribed later, and is specified by the light emitting pulse controlsignal EC.

In the light emitting format A, the total number of light emittingpulses is 1275, five light emitting pulses are assigned to the sub-fieldSF1, 10 light emitting pulses are assigned to the sub-field SF2, and 20,40, 80, 160, 320, and 640 light emitting pulses are similarly assigned,respectively, to the sub-fields SF3 to SF8.

The total number of light emitting pulses is 1020 in the light emittingformat B, the total number of light emitting pulses is 765 in the lightemitting format C, the total number of light emitting pulses is 510 inthe light emitting format D, and the total number of light emittingpulses in the light emitting format E is 255. The number of lightemitting pulses, as shown, is assigned to each of the sub-fields SF1 toSF8.

When the sub-fields SF1 to SF8 are combined to perform display on 256gray scales, therefore, the light emitting formats A to E differ in thenumber of light emitting pulses and luminance even at the same grayscale level. That is, when the luminance in the light emitting format Eis used as a basis (once), the luminance in the light emitting format Dis twice that in the light emitting format E, the luminance in the lightemitting format C is three times that in the light emitting format E,the luminance in the light emitting format B is four times that in thelight emitting format E, and the luminance in the light emitting formatA is five times that in the light emitting format E. Consequently, thelight emitting formats are successively switched from A to E, therefore,the luminance of the display screen can be lowered without significantlychanging the total number of gray scales.

Description is now made of the relationship between a temperaturedifference estimated value Td and a multiplication factor k in a casewhere the light emitting formats A to E are combined with each other toinduce sustain discharges. FIG. 8 is a diagram showing the relationshipbetween a temperature difference estimated value Td and a multiplicationfactor k in a case where the light emitting formats A to E are combinedwith each other to induce sustain discharges. The relationship betweenthe temperature difference estimated value Td and the multiplicationfactor k shown in FIG. 8 is previously stored in the controller 3. Thelight emitting format and the multiplication factor k which correspondto the temperature difference estimated value Td estimated by thetemperature difference estimator 4 are specified by the controller 3.

As shown in FIG. 8, in the light emitting format A, as the temperaturedifference estimated value Td increases, the multiplication f actor klinearly decreases from 1.0 to 0.8. Then, in the light emitting formatB, as the temperature difference estimated value Td increases, themultiplication factor k decreases from 1.0 to 0.75. Then, in the lightemitting format C, as the temperature difference estimated value Tdincreases, the multiplication factor k decreases from 1.0 to 0.67. Then,in the light emitting format D, as the temperature difference estimatedvalue Td increases, the multiplication factor k decreases from 1.0 to0.5. Finally, in the light emitting format E, as the temperaturedifference estimated value Td increases, the multiplication factor kdecreases from 1.0.

From the following reason, the multiplication factor is returned to 1.0when the light emitting format is switched after decreasing from 1.0.That is, the total number of light emitting pulses in the light emittingformat A is 1275, and the total number of light emitting pulses in thelight emitting format B is 1020. Accordingly, the ratio of the numbersof pulses is 0.8. When the light emitting format is switched from A toB, therefore, the multiplication factor k is switched from 0.8 to 1.0,thereby making it possible to reduce the number of light emitting pulsesat a predetermined ratio depending on the temperature differenceestimated value Td before and after the switching and to linearlycontrol the luminance of the display screen. The same is true even atthe time of later switching the light emitting format.

The multiplication factor k is thus switched depending on the totalnumber of light emitting pulses at the time of switching the lightemitting format, thereby making it possible to linearly control theluminance of the display screen depending on the temperature differenceestimated value Td even when the image is displayed using the differentlight emitting format as well as to lower the luminance withoutextremely reducing the total number of gray scales.

When the video signal VS is multiplexed by the multiplication factor k,to display the image using the video signal, the temperature differenceestimated value Td increases, and the luminance after the controllinearly decreases, as shown in FIG. 9, thereby making it possible tolower the luminance of the display screen depending on the temperaturedifference estimated value Td. In FIG. 9, the luminance in a case wherethe luminance is not decreased, that is, the temperature differenceestimated value Td is zero is 5 (a relative value).

The light emitting format is not particularly limited to theabove-mentioned example. The sustain discharges may be induced usingonly the light emitting format A out of the light emitting formats A toE. FIG. 10 is a diagram showing the relationship between the temperaturedifference estimated value Td and the multiplication factor k in a casewhere the light emitting format A is used. When the temperaturedifference estimated value Td is zero, that is, the temperature is notraised, as shown in FIG. 10, the multiplication factor k is outputted as1.0. As the temperature difference estimated value Td increases, themultiplication factor k linearly decreases. Consequently, the videosignal VS is multiplexed by the multiplication factor k by themultiplication circuit 21, thereby making it possible to lower theluminance of the display screen depending on the temperature differenceestimated value Td, as in a case shown in FIG. 9.

Description is now made of a first luminance control method for theplasma display device configured as described above.

First in the temperature difference estimator 4, a video signal for theperiphery adjacent portion is separated from a video signal VS by theperiphery adjacent portion separator 41, a luminance signal in the videosignal for the periphery adjacent portion is integrated by theintegration circuit 42, and the amount of dissipated heat is subtractedby the dissipated heat subtraction circuit 43, to calculate atemperature estimated value Te for the periphery adjacent portion. Areference value To for the panel outer periphery set by the panelperiphery temperature setter 5 is subtracted from the temperatureestimated value Te for the periphery adjacent portion by the subtracter44, so that a temperature difference estimated value Td for theperiphery of the display screen is calculated.

As shown in FIG. 8, a light emitting format and a multiplication factork which correspond to the temperature difference estimated value Td arethen determined by the controller 3, so that a light emitting pulsecontrol signal EC corresponding to the determined light emitting formatand a brightness control signal LC including the determinedmultiplication factor k are generated.

Then in the brightness controller 2, the video signal VS is multipliedby the multiplication factor k included in the brightness control signalLC by the multiplication circuit 21, so that a video signal whoseluminance has been controlled is generated depending on themultiplication factor k. Image data for each sub-field in the lightemitting format corresponding to the light emitting pulse control signalEC included in the brightness control signal LC is then generated fromthe video signal corresponding to one field whose luminance has beencontrolled by the video signal/sub-field corresponder 22, and a datadriver driving control signal DS corresponding to the image data isoutputted. Further, a scan driver driving control signal CS and asustain driver driving control signal US which correspond to eachsub-field in the light emitting format corresponding to the lightemitting pulse control signal EC are generated by the sub-field pulsegenerator 23.

Finally, in the display 1, address discharges in the correspondingdischarge cell are induced in response to the data driver drivingcontrol signal DS and the scan driver driving control signal CS by thedata driver 12 and the scan driver 13, and sustain discharges are theninduced in the discharge cell in which the address discharges have beeninduced in response to the scan driver driving control signal CS and thesustain driver driving control signal US by the scan driver 13 and thesustain driver 14. Accordingly, an image is displayed on the displayscreen with the luminance controlled depending on the multiplicationfactor k. The larger the temperature difference estimated value Tdbecomes, the lower the luminance of the display screen becomes.

As described in the foregoing, in the luminance control method, thetemperature estimated value Te corresponding to the temperature of theperiphery adjacent portion of the display screen of the PDP 11 isestimated from the video signal VS, the temperature difference estimatedvalue Td is found using the temperature estimated value Te and thereference value To corresponding to the temperature of the panel outerperiphery, the light emitting format and the multiplication factor kwhich correspond to the temperature difference estimated value Td aredetermined, and the luminance of the display screen of the PDP 11 iscontrolled by the light emitting format and the multiplication factor kwhich have been determined. Consequently, the luminance can becontrolled on the basis of the temperature difference between the panelouter periphery which greatly affects the damage to the PDP 11 and theperiphery adjacent portion closest to the panel outer periphery, therebymaking it possible to more reliably prevent the PDP 11 from beingdamaged. Further, only the temperature estimated value Td for theperiphery adjacent portion is operated, so that the amount of operationis reduced, thereby making it possible to simplify the processing aswell as to shorten the processing time.

Description is now made of a second luminance control method for theplasma display device. The second luminance control method is a methodof dividing the display screen into a plurality of blocks andcontrolling the luminance of the peripheral block adjacent to the outerperiphery of the display screen out of the blocks obtained by thedivision. The control method is carried out by the controller 3outputting a multiplication factor k corresponding to a temperaturedifference estimated value Td when a video signal VS corresponding tothe peripheral block is inputted to the multiplication circuit 21,outputting one as the multiplication factor k when the video signal VScorresponding to the inner block other than the peripheral block isinputted to the multiplication circuit 21, and multiplying the videosignal VS by the multiplication factors k by the multiplication circuit21. In this case, a vertical synchronizing signal and a horizontalsynchronizing signal, for example, are inputted to the controller 3through the temperature difference estimator 4, and the display screenis divided using the horizontal synchronizing signal and the verticalsynchronizing signal, for example, to specify the peripheral block.

FIG. 11 is a diagram showing an example of a multiplication factor k foreach block in a case where the luminance of the peripheral block iscontrolled. In the following, description is made of a case where thedisplay screen is divided into a total of 25 blocks, that is, fiveblocks in the longitudinal direction and five blocks in the transversedirection. However, the number of divisions of the display screen is notparticularly limited to that in this example. The number can be suitablydetermined depending on the number of pixels composing the displayscreen, and the processing capabilities of the temperature differenceestimator 4, the controller 3, and so forth, for example. In FIG. 11, adischarge cell in the outermost periphery is positioned in the outermostperiphery of each peripheral block, and an outer frame indicates theouter periphery of the PDP 11.

In the example shown in FIG. 11, the multiplication factor k for theperipheral blocks (blocks indicated by hatching) is set to 0.5, and themultiplication factor k for the outer inner blocks is set to one. Inthis case, the multiplication factor k is decreased only in a portion ofthe peripheral block most easily damaged, and the luminance of thisportion is reduced. Consequently, the PDP 11 can be more reliablyprevented from being damaged without lowering the luminance of theinside of the display screen.

Description is now made of a third luminance control method for theplasma display device. The third luminance control method is a method ofcontrolling the luminance of each of blocks such that the luminance ofthe peripheral block is made lower than that of the inner block. Thecontrol method is carried out by the controller 3 outputting amultiplication factor k corresponding to a temperature differenceestimated value Td when a video signal VS corresponding to theperipheral block is inputted to the multiplication circuit 21,increasing the multiplication factor k depending on the position of eachof the blocks such that the multiplication factor for the block at thecenter is one when the video signal VS corresponding to the inner blockother than the peripheral block is inputted to the multiplicationcircuit 21, and multiplying the video signal VS by the multiplicationfactor k by the multiplication circuit 21.

FIG. 12 is a diagram showing an example of the multiplication factor kfor each block in a case where the luminance of the blocks is controlledsuch that the luminance of the peripheral blocks is made lower than thatof the inner blocks. In the example shown in FIG. 12, the multiplicationfactor k for the peripheral blocks is set to 0.5, the multiplicationfactor k for the inner blocks is set to 0.75, and the multiplicationfactor k for the block at the center is set to one. In this case, theluminance of a portion of the peripheral block most easily damaged ismost greatly reduced, thereby making it possible to more reliablyprevent the PDP 11 from being damaged. Since the multiplication factor kis gradually decreased toward the outer periphery of the PDP 11, thechange in the luminance by the change in the multiplication factor k isdifficult to visually know, thereby making it possible to prevent theimage quality from being degraded. The amount of change of themultiplication factor k depending on the position of the block is notparticularly limited to that in the above-mentioned example. Variousmodifications are possible. For example, the amount of change on theside of the outer periphery is made larger.

Description is now made of a plasma display device according to a secondembodiment of the present invention. FIG. 13 is a block diagram showingthe configuration of the plasma display device according to the secondembodiment of the present invention.

The plasma display device shown in FIG. 13 divides a display screen of adisplay 1 into a plurality of blocks, finds a peripheral blocktemperature difference estimated value Tbd for each peripheral blockadjacent to the outer periphery of the display screen out of the blocksobtained by the division, and controls luminance using the peripheralblock temperature difference estimated value Tbd. Consequently, theplasma display device shown in FIG. 13 is the same as the plasma displaydevice shown in FIG. 1 except that the temperature difference estimator4 is changed into a temperature difference estimator 4A for estimatingthe peripheral block temperature difference estimated value Tbd for eachperipheral block. Accordingly, the same portions are assigned the samereference numerals and hence, the description thereof is not repeated.Only the temperature difference estimator 4A obtained by the change willbe described in detail.

FIG. 14 is a block diagram showing the configuration of the temperaturedifference estimator 4A shown in FIG. 13. The temperature differenceestimator 4A shown in FIG. 14 is the same as the temperature differenceestimator 4 shown in FIG. 2 except that a block separator 45 is addedbetween a periphery adjacent portion separator 41 and an integrationcircuit 42. Accordingly, the same portions are assigned the samereference numerals and hence, the description thereof is not repeated.

As shown in FIG. 14, the block separator 45 is connected to theperiphery adjacent portion separator 41, and receives a video signal fora periphery adjacent portion which is outputted from the peripheryadjacent portion separator 41, separates the video signal for eachperipheral block adjacent to the outer periphery of the display screen,and outputs the divided video signal to the integration circuit 42. Inthis case, a vertical synchronizing signal and a horizontalsynchronizing signal, for example, included in the video signal VS areinputted to the block separator 45, so that the peripheral block isextracted using the horizontal synchronizing signal and the verticalsynchronizing signal, for example. In a stage succeeding the integrationcircuit 42, each processing is performed, as in the first embodiment,for each peripheral block. Finally, the peripheral block temperaturedifference estimated value Tbd is outputted for each peripheral blockfrom a subtracter 44.

FIG. 15 is a diagram showing an example of a temperature estimated valueTb and a peripheral block temperature difference estimated value Tbdwhich are estimated for each peripheral block. Although in thefollowing, description is made of a case where the display screen isdivided into five blocks in the longitudinal direction and five blocksin the transverse direction, and the block adjacent to the outerperiphery of the display screen out of the blocks obtained by thedivision is taken as a peripheral block, the number of divisions of thedisplay screen is not particularly limited to that in this example. Thenumber can be suitably determined depending on the number of pixelscomposing the display screen, and the processing capabilities of thetemperature difference estimator 4A, the controller 3, and so forth, forexample. In FIG. 15, a discharge cell in the outermost periphery ispositioned in the outermost periphery of the peripheral block, and anouter frame indicates the outer periphery of a PDP 11.

As shown in FIG. 15(a), the temperature estimated value Tb is determinedfor each peripheral block. For example, the temperature estimated valueTb for the peripheral block in the upper left of the display screen is17, the temperature estimated value Tb for the peripheral block adjacentthereto on the right side is 18, and the temperature estimated value Tbfor the peripheral block adjacent thereto on the right side is 20. Thetemperature estimated value Tb is thus estimated for each peripheralblock.

A reference value To is subtracted from each of the temperatureestimated values Tb shown in FIG. 15(a). In this example, the referencevalue To for the peripheral blocks included in two rows in an upper partUR is set to 10, and the reference value To for the peripheral blocksincluded in three rows in a lower part DR is set to five. Consequently,the peripheral block temperature difference estimated value Tbd for eachof the peripheral blocks from which each of the reference values hasbeen subtracted is a value shown in FIG. 15(b). A multiplication factork is determined, as in FIG. 8, for each of the peripheral blocks usingthe value, and the luminance of the peripheral block is controlleddepending on the multiplication factor k.

Generally in the PDP 11, an address electrode AD is wired to its upperpart, as shown in FIG. 5. Accordingly, a vent for cooling, for example,is provided in its lower part. The temperature of the upper part tendsto be raised more easily, as compared with the temperature of the lowerpart. Consequently, a high reference value is set with respect to theupper part UR in the PDP 11, and a lower reference value is set in thelower part DR, as compared with that in the upper part UR, therebymaking it possible to calculate a temperature difference estimated valuecloser to thermal stress actually created in the panel outer peripheryof the PDP 11. As a result, the PDP 11 can be more reliably preventedfrom being damaged, and the luminance is not lowered any more thannecessary. A method of controlling luminance using a plurality ofreference values which differ depending on the position of the panelouter periphery of the PDP 11, as described above, is also applicable toother embodiments.

The controller 3 uses the peripheral block temperature differenceestimated value Tbd for each peripheral block found in theabove-mentioned manner, to output a brightness control signal LC to abrightness controller 2 such that luminance is controlled for eachperipheral block. The brightness controller 2 outputs to the display 1an address driver driving control signal AD, a scan driver drivingcontrol signal CS, and a sustain driver driving control signal US forcontrolling the luminance for each peripheral block in response to abrightness control signal LC. In the display 1, the luminance iscontrolled for each peripheral block in response to each of the inputteddriving control signals by each luminance control method describedbelow.

The present embodiment is the same as the first embodiment except thatthe temperature difference estimator 4A corresponds to a temperatureestimation circuit and an operation circuit, and the block separator 45corresponds to a block extraction circuit.

A first luminance control method for the plasma display deviceconfigured as described above will be described. The first luminancecontrol method is a method of estimating a temperature estimated valueTb for each peripheral block, subtracting a reference value To from thetemperature estimated value Tb for the peripheral block to find aperipheral block temperature difference estimated value Tbd, andcontrolling luminance depending on the peripheral block temperaturedifference estimated value Tbd for the peripheral block. Also in thecontrol method, a multiplication factor k corresponding to theperipheral block temperature difference estimated value Tbd for theperipheral block is outputted when a video signal VS corresponding tothe peripheral block separated by the block separator 45 is inputted toa multiplication circuit 21, one is outputted as the multiplicationfactor k when the video signal VS corresponding to the inner block otherthan the peripheral block is inputted to the multiplication circuit 21,and the video signal VS is multiplied by the multiplication factors k bythe multiplication circuit 21.

FIG. 16 is a diagram showing an example of a peripheral blocktemperature difference estimated value Tbd and a multiplication factorfor each peripheral block in a case where luminance is controlled forthe peripheral block by the first luminance control method.

First, as shown in FIG. 16(a), it is assumed that a peripheral blocktemperature difference estimated value Tbd is estimated for eachperipheral block. That is, it is assumed that the peripheral blocktemperature difference estimated value Tbd for the peripheral blockspositioned at the respective centers of the upper side, the lower side,the left side, and the right side of the display screen is 20, and theperipheral block temperature difference estimated value Tbd for theother peripheral blocks is zero. In this case, a multiplication factor kfor the peripheral block is as shown in FIG. 16(b). That is, themultiplication factor k for the peripheral blocks at the respectivecenters of the upper side, the lower side, the left side, and the rightside is 0.5, and the multiplication factor k for the other peripheralblocks is one. The luminance of each of the peripheral blocks iscontrolled depending on the multiplication factor k.

In this case, the multiplication factor k is decreased only in theperipheral block where the peripheral block temperature differenceestimated value Tbd is large, and only the luminance of this portion isreduced. Consequently, only the luminance of the peripheral block mosteasily damaged is lowered without lowering the luminance of the otherblock, thereby making it possible to more reliably prevent the PDP 11from being damaged.

A second luminance control method for the plasma display device will bedescribed. The second luminance control method is for controllingluminance for each peripheral block on the basis of a peripheral blocktemperature difference estimated value Tbd′ obtained by subjecting aperipheral block temperature difference value Tbd between adjacentperipheral blocks to filtering processing such that the amount ofcontrolled luminance between the adjacent peripheral blocks is smoothlychanged. In the control method, the peripheral block temperaturedifference estimated value Tbd is subjected to filtering processing suchas integration or interpolation between the adjacent peripheral blocksby the controller 3, a multiplication factor k corresponding to theperipheral block temperature difference estimated value Tbd′ after thefiltering processing is outputted, and a video signal VS correspondingto the peripheral block is multiplied by the multiplication factor k inthe multiplication circuit 21.

FIG. 17 is a diagram showing an example of a peripheral blocktemperature difference estimated value Tbd for each peripheral block, aperipheral block temperature difference estimated value Tbd′ afterfiltering processing, and a multiplication factor k in a case whereluminance is controlled for each peripheral block such that the amountof controlled luminance is smoothly changed by the second luminancecontrol method.

First, as shown in FIG. 17(a), it is assumed that a peripheral blocktemperature difference estimated value Tbd is estimated for eachperipheral block, as in FIG. 16(a). The peripheral block temperaturedifference estimated value Tbd is then filtered by interpolation betweenthe adjacent peripheral blocks. The peripheral block temperaturedifference estimated value Tbd′ after the filtering processing is asshown in FIG. 17(b). A peripheral block. temperature differenceestimated value Tbd for the peripheral block between the peripheralblock having a peripheral block temperature difference estimated valueTbd of 20 and the peripheral block having a peripheral block temperaturedifference estimated value Tbd of 0 is interpolated from zero to 10. Inthis case, a multiplication factor k for each of the peripheral blocksis as shown in FIG. 17(c). That is, the multiplication factor k for theperipheral blocks at the respective centers of the upper side, the lowerside, the left side and the right side is 0.5, the multiplication factork for the peripheral block positioned at each vertex of the displayscreen is one, and the multiplication factor k for the intermediateperipheral block is 0.75. The multiplication factor k is smoothlychanged. The luminance of each of the peripheral blocks is controlleddepending on the multiplication factor k.

In this case, the luminance of a portion of the peripheral block mosteasily damaged is most greatly reduced, and thermal stress in theperipheral block is smoothly changed, thereby making it possible to morereliably prevent the PDP 11 from being damaged. Further, themultiplication factor k is gradually smoothly changed. Accordingly, thechange in the luminance by the change in the multiplication factor k isdifficult to visually know, thereby making it possible to prevent theimage quality from being degraded. The change in the multiplicationfactor k by the filtering processing is not particularly limited.Various modifications are possible. For example, the multiplicationfactor k is exponentially changed.

Description is now made of a plasma display device according to a thirdembodiment of the present invention. FIG. 18 is a block diagram showingthe configuration of the plasma display device according to the thirdembodiment of the present invention.

The plasma display device shown in FIG. 18 divides a display screen of adisplay 1 into a plurality of blocks, finds a peripheral blocktemperature difference estimated value Tbd for each peripheral blockadjacent to the outer periphery of the display screen out of the blocksobtained by the division, extracts the maximum peripheral blocktemperature difference estimated value Tmax out of the peripheral blocktemperature difference estimated values Tbd, and controls luminanceusing the maximum peripheral block temperature difference estimatedvalue Tmax. Consequently, the plasma display device shown in FIG. 18 isthe same as the plasma display device shown in FIG. 13 except that thetemperature difference estimator 4A is changed into a temperaturedifference estimator 4B for estimating the peripheral block temperaturedifference estimated value Tbd for each peripheral block and extractingthe maximum peripheral block temperature difference estimated valueTmax. Accordingly, the same portions are assigned the same referencenumerals and hence, the description thereof is not repeated. Only thetemperature difference estimator 4B obtained by the change will bedescribed in detail.

FIG. 19 is a block diagram showing the configuration of the temperaturedifference estimator 4B shown in FIG. 18. The temperature differenceestimator 4B shown in FIG. 18 is the same as the temperature differenceestimator 4A shown in FIG. 14 except that a maximum selector 46 is addedin a stage succeeding a subtracter 44. Accordingly, the same portionsare assigned the same reference numerals and hence, the descriptionthereof is not repeated.

As shown in FIG. 19, the maximum selector 46 is connected to thesubtracter 44, and selects a maximum peripheral block temperaturedifference estimated value Tb out of the peripheral block temperaturedifference estimated values Tbd for the peripheral blocks in one field,that is, one display screen which are outputted from the subtracter 44and extracts the maximum peripheral block temperature differenceestimated value Tbd as a maximum peripheral block temperature differenceestimated value Tmax.

FIG. 20 is a diagram showing an example of a temperature estimated valueTb, a peripheral block temperature difference estimated value Tbd, and amaximum peripheral block temperature difference estimated value Tmaxwhich are estimated for each peripheral block.

As shown in FIG. 20(a), it is assumed that a temperature estimated valueTb is estimated for each peripheral block, as in FIG. 15(a). As shown inFIG. 20(b), a peripheral block temperature difference estimated valueTbd for each peripheral block is then found, as in FIG. 15(b). Finally,a peripheral block at the lower left corner having a maximum peripheralblock temperature difference estimated value Tbd (13 in the exampleshown in FIG. 20) out of peripheral block temperature differenceestimated values Tbd shown in FIG. 20(b) is selected, and 13 which isthe peripheral block temperature difference estimated value Tbd for theperipheral block is taken as the maximum peripheral block temperaturedifference estimated value Tmax.

As a result, as shown in FIG. 20(C), the peripheral block temperaturedifference estimated values Tbd for all the peripheral blocks arereplaced with the maximum peripheral block temperature differenceestimated value Tmax. A multiplication factor k is determined, as inFIG. 8, for each peripheral block using the maximum peripheral blocktemperature difference estimated value Tmax, and the luminance of eachof the peripheral blocks is controlled depending on the multiplicationfactor k.

A controller 3 uses the maximum peripheral block temperature differenceestimated value Tmax found in the above-mentioned manner, to output abrightness control signal LC to a brightness controller 2 such that theluminance is controlled for each peripheral block. The brightnesscontroller 2 outputs to a display 1 an address driver driving controlsignal AD, a scan driver driving control signal CS, and a sustain driverdriving control signal US for controlling luminance for each peripheralblock depending on the brightness control signal LC. In the display 1,the luminance is controlled in response to each of the inputted drivingcontrol signals.

The present embodiment is the same as the second embodiment except thata temperature difference estimator 4B corresponds to a temperatureestimation circuit and an operation circuit.

In the plasma display device configured as described above, theluminance control method for each of the above-mentioned embodiments canbe used, thereby making it possible to obtain the same effect.

In the present embodiment, the luminance is controlled using the maximumperipheral block temperature difference estimated value Tmaxrepresenting the largest temperature difference in the peripheralblocks, thereby making it possible to more reliably prevent the PDP 11from being damaged. Further, the luminance is controlled by one maximumperipheral block temperature difference estimated value, so thatprocessing for controlling the luminance is simplified.

Description is now made of a plasma display device according to a fourthembodiment of the present invention. FIG. 21 is a block diagram showingthe configuration of the plasma display device according to the fourthembodiment of the present invention.

The plasma display device shown in FIG. 21 is the same as the plasmadisplay device shown in FIG. 1 except that a temperature measuring unit6 is added. Accordingly, the same portions are assigned the samereference numerals and hence, the description thereof is not repeated.

As shown in FIG. 21, the temperature measuring unit 6 is connected to apanel periphery temperature setter 5, and directly measures thetemperature of the panel outer periphery of a PDP 11 and outputs themeasured temperature to the panel periphery temperature setter 5. Thepanel periphery temperature setter 5 sets a reference value Tocorresponding to the measured temperature and outputs the set referencevalue To to a temperature difference estimator 4. After that, thesubsequent processing is performed, as in the first embodiment, so thatluminance is controlled.

The present embodiment is the same as the first embodiment except thatthe panel periphery temperature setter and the temperature measuringunit 6 correspond to a measurement circuit.

In the plasma display device configured as described above, theluminance control method in the first embodiment can be similarly used,thereby making it possible to obtain the same effect. When thetemperature measuring unit 6 in the present embodiment is used foranother embodiment, a luminance control method in another embodiment canbe also similarly used, thereby making it possible to obtain the sameeffect.

In the present embodiment, the temperature of the panel outer peripheryis directly measured, and the luminance can be controlled on the basisof the reference value To corresponding to the temperature. Even whenthe reference value To is changed due to the variation in outer airtemperature, for example, therefore, the PDP 11 can be more reliablyprevented from being damaged. The number of measuring points in thetemperature measuring unit 6 may be one of plural in the panel outerperiphery. When a plurality of points are measured, a reference valuemay be set for each of the measuring points, or a reference value may beset, for example, with respect to the average of the results of themeasurement of the plurality of points.

Although in each of the above-mentioned embodiments, the video signal VSis multiplexed by the multiplication factor k included in the brightnesscontrol signal LC outputted from the controller 3 in the multiplicationcircuit 21 to control the luminance, the maximum luminance of an imagedisplayed on the PDP 11 may be lowered by changing the multiplicationcircuit 21 into a limiting circuit for limiting the maximum luminance ofthe video signal, outputting an upper-limit value of the maximumluminance corresponding to the temperature difference estimated valuefrom the controller 3, and limiting only luminance exceeding theupper-limit value of the maximum luminance by the limiting circuit.

1. A display device, comprising: a display having a display screen thatdisplays an image with a luminance corresponding to a video signal andan outer peripheral portion adjacent to said display screen; atemperature estimation device that provides a temperature estimationvalue, corresponding to a temperature of said display screen, based uponsaid video signal; an operation device that determines a temperaturedifference estimation value using a reference value corresponding to thetemperature of said outer peripheral portion and said temperatureestimation value; and a control device that controls said luminance onsaid display screen so as to lower a maximum luminance of said image assaid temperature difference estimation value increases.
 2. The displaydevice of claim 1, wherein said temperature estimation device estimatessaid temperature estimation value corresponding to a temperature of anouter periphery adjacent portion in said display screen adjacent to saidouter peripheral portion.
 3. The display device of claim 1, wherein saiddisplay comprises a first board and a second board whose outerperipheries are joined to each other, a plurality of light emittingelements that form said display screen being interposed between saidfirst board and said second board, said outer peripheral portion of saiddisplay including a portion between said light emitting elementspositioned in an outermost periphery of said display screen and a jointportion of said first board and said second board.
 4. The display deviceof claim 1, wherein said temperature estimation value is estimated byintegrating data related to said luminance from said video signal andsubtracting data corresponding to an amount of dissipated heat from saidintegrated data, said operation device subtracting said reference valuefrom said temperature estimation value to determine said temperaturedifference estimation value.
 5. The display device of claim 1, whereinsaid image is displayed on said display screen with a gray scale,selected from a plurality of gray scales, corresponding to said videosignal, said control device lowering said luminance of said image at asame ratio for each of said plurality of gray scales.
 6. The displaydevice of claim 1, wherein said reference value comprises one referencevalue selected from a plurality of reference values, said plurality ofreference values differing from one another based upon a position of anouter peripheral portion of said display.
 7. The display device of claim1, further comprising: a measurement device that measures saidtemperature of said outer peripheral portion of said display, saidmeasurement device outputting said reference value, corresponding tosaid measured temperature, to said operation device.
 8. A method forcontrolling a luminance of a display device, the display device having adisplay screen that displays an image with a luminance corresponding toa video signal, and an outer peripheral portion adjacent to said displayscreen, the method comprising: obtaining a temperature estimation value,that corresponds to a temperature of the display screen, from the videosignal; finding a temperature difference estimation value using areference value, that corresponds to a temperature of the outerperipheral portion, and the temperature estimation value; and lowering amaximum luminance of the image as the temperature difference estimationvalue increases.
 9. A display device, comprising: a display having adisplay screen that displays an image with a luminance corresponding toa video signal and an outer peripheral portion adjacent to said displayscreen; a temperature estimation device that provides a temperatureestimation value, corresponding to a temperature of said display screen,based upon said video signal; an operation device that determines atemperature difference estimation value using a reference valuecorresponding to the temperature of said outer peripheral portion andsaid temperature estimation value; and a control device that controlsthe luminance of the image based on the temperature differenceestimation value.